@~x{sigil}modifiers[key: value]
@~x{sigil}modifiers [key: value]
@~x{sigil}modifiers[()]
@~x{sigil}modifiers [()]
@~x{sigil}modifiers[matched_expression]
@~x{sigil}modifiers [matched_expression]
@~x{sigil}modifiers[matched_expression,]
@~x{sigil}modifiers [matched_expression,]
